Process of treating rubber and product obtained thereby



Patented Got. 14, 1930 .iraras PATENT OFFICE SIDNEY M. CADWELL, orLEONIA, new JERsnY, ASSIGNOR TO THE NAUGATUCK CHEMICAL COMPANY, orNAUGATUCK,.GO1\TNECTIGUT, A CORPORATION or CON- NECTICU'I PROCESSOFTREATING.- RUBBEE AND PRODUCT OBTAINED THEREIBY No Drawing.

This invention relates to the treatment of rubberand similar materialsand to the proclucts obtained thereby. The invention is moreparticularly concerned with new classes of chemical compounds capableofv functioning as accelerators of vulcanization.

This case is a division of copending application Serial No. 258,670, andSerial No. 258,675, filed of even date.

Accordingly the objects of the invention include the vulcanization ofrubber treated with the hereinafter described classes of compounds.Another object is to provide new chemical compounds, particularly usefulin vulcanization, which are comparatively inexpensive and at the sametime highly eflicient both from the standpoint of their behavior duringthe compounding of rubber as well as in the properties which they impartto the vulcanized product. Another object of the invention is toaccelerate the action of the new chemical compounds by theaddition ofbase or to retardtheir action by the addition of acid material. Afurther object of the invention is to provide a method whereby the acidor base or the new compounds themselves may be introduced into rubber.

In the present practice of the use of accelerators, it is generallyknown that many of the compounds employed are so powerful that theycause a prevulcanization, or burnino' on the mixing mill. This seriousdisadvantage is possessedby many of the accelerators which have theproperty of vulcanizing rubber at ordinary temperatures or atte1nperatures well below those ordinarily employed in hotvulcanization,for example at 212 F. or thereabouts. Illustrations of such rapidaccelerators are metallic dithiocarbamates, metallic salts of otherthioacids, mercapto thiazoles and the like. According to the presentinvention this serious objection of prevulcanization may be entirelyovercome, the rubber compounds may be mixed upon the mill withpractically no danger of prevulcanization thereon, without sacrificingthe accelerating power which is desired. Certain of the compoundsforming the subject matter of the present invention may be mixed withentire safety on themixing mills, sub- Application filed March 2, 1928.Serial No. 258,679.

ject to the, conditions hereinafter named, whereas others may be safelymixed, observing certain precautions as to mill temperatures, etc. r

The invention includes combining rubber and similar vulcanizablematerials with a vulcanizing combination, including a vulcanizing agent,a metallic oxide or its equivalent and a 2-6 dinitro d-chloro phenylthiol derivative of a. substituted dithiocarbamate, and vulcanizing therubber. The invention also includes the products thus obtained, and thepreparation of the chemical compounds as well. I r

The invention further consists in accelerating the action of thecompounds by the ad dition of basic materials and in retarding theaction ofthe compounds and particularly the burning of the compounds bythe addition of acid materials. The invention further consists inintroducing basic materials or acid materials or the compounds hereindisclosed by diffusion from rubber or from any surrounding medium.

The whole compond, 2-6 dinitro et-chloro phenyl dialkyl dithiocarbamatereacts at least as rapidly with sodium hydroxide in boiling aqueousalcohol as diphenylmethyl dimethyl dithiocarbamate reacts under the sameconditions. All the compounds which react with s dium hydroxide at leastas rapidly as diphenylmethyl dimethyl dithiocarbamate (M. P. 96.597 (l),accelerates vulcanization, in the presence of a metallic oxide, such aszinc oxide or an equivalent metallic compound; Those compounds which donot hydrolyze at such a rate do not accelerate vulcanization. I

Zinc oxide is a good illustration of a metallic oxide which may be used.In place of zinc the following elements may be used in combined form,preferably somewhat basic and soluble in rubber; mercury preferably inthe mercuric state, lead preferably in the plumbous state, cadmium,copper, preferably in the oupric state, arsenic preferably in thearsenous state, manganese preferably in the manganous state. Preferablythe metallic compound is ofsuch a nature that the metallic element isavailablezduring the vulcanization process. Oxides, stearates,carbonates are among the metallic compounds which may be used.

As one illustration of the invention, 100 parts of pale crepe, 10 partsof zinc o.:ide, 3 parts of sulphur, and 0.3 part of 2-6 dinitr 4. chlorophenyl dimethyl (lithio carbamate may be mixed togetl'ierin thecustomary way on a mixing mill or in any other desired manner. Therubber stock thus prepared is well vulcanized in 60 minutes at 20 lbs.steam pressure. The stock may also be vulcanized at higher steampressures than 20 lbs.

24) dinit-ro l-chloro phenyl dimethyl dithiocarbamate is a new compound.One method of preparing it is L s follows:

grams of dimethylamine are dissolved in 1000 cc. of alcohol and to thissolution are added 76 grams of carbon disulphide. file this mixture arethen added 40 of c tic soda dissolved in a small amountof v. ter, thewhole mixture being kept cool throughout. The result is an alcoholicsolution of sodium dimethyl dithiocarbamate. To this mixture are thenadded 237 grains of 52-6 dinitro 1, 4 dichlorobenzol and the wholeheated to -60 C. for of an hour. The reaction mixture is then cooled andthe pri l uct which is the 2-6 dinitro 4 chlorophenyl dimethyldithiocarbamate crystallizes out. It is filtered from the alcohol,washed free from sodium chloride and dried.

The corresponding diethyl dithiocarbamate, etc., may be similarlyprepared. in these compounds, one nitro group is ortho to the OS bond ofthe compound, and at least one of the remaining substituents, forexample, the other nitro group, is meta to the aforesaid nitro group.

2-6 dinitro -chloro phenyl dimethyl dithiocarbamate functions well whenthe cure is carried out according to any of the commercial methods, suchas in steam, talc, water, etc. Other dialkyl dithiocarbamates may )8employed, provided they satisfy the conditions of hydrolysis herein setforth.

I have observed that the action of the compounds disclosed herein isparticularly accelerated by the presence of a small amount of a basicmaterial such as sodium hydroxide, trisodium phosphate, dicyandiamide,piperidine, aniline, dibenzylamine, piperazinchydrate, triethanolamine.The use of the base lowers the temperature at which the acceleratorfunctions or increases its speed fa etioning and usually increases thetens strength at all temperatures of vulcanization by about 10%.

lhe base may be employed in amounts generally less than 1% orthereabouts.

Since a basic material accelerates the action of the accelerator a .dlowers the temper ature at which it functions, it also increases thespeed of burning on the mixing mill. Therefore the greater the amount ofbase present in the mix, the greater the danger of burning on the mixingmill and rubbers which are basic therefore accelerate the action ofthese compounds. Burning on the mixing mill is one form of what isherein called premature vulcanization. llhe latter expression alsoincludes the burning, scorching, or setting up of the stock on mills,ealenders, tubing machines, as well any pnevulcanization which may ccuror be incipient prior to the actual deliberate vuleanization operation.T his is particularly true of the dinitrophenyl compounds.

On the other hand the addition of acid retards the action of theaccelerator and therefore improves its resistance to burning.

For example .1 part of monochlor acetic acid added to the above stockminimizes any danger of burning on the mill, but at the same tin doesretard the rate of vulcanization. With larger amounts of acid it ispossible to retard vulcanization almost to the point where novulcanization takes place. Other acids which I have successfully employed are sulphanilic, oxalic, picric, phosphoric, trichloracetic, paratoluene sulphonyl chloride and pine tar. I have also successfullyemployed substances which may form acids during the course ofvulcanization such as ethyl oxalate, or zinc acetate.

Mixes which are slightly acid because of the presence of carbon black orpine tar resist burning on the mill abnormally well. The ulcanization ofrubbers which are acid by nature, or contain appreciable amounts of acidor acidic ingredients is not accelerated by the herein describedcompounds, unless the acidic properties be first removed or neutralized.

Likewise, rubbers or rubber stocks which are appreciably basic bynature, or contain basic materials, may display a. marked, oftenundesirable tendency towards prevulcanization. Such basic rubbers orstocks may be treated with acidic material to remove, to curb, or tocontrol this tendency to prevulcanize. Therefore, by the use of basicmaterial and acidic material in suitable proportions arequired, anyrubber or stock may be brought to aprcdetermined speed of vulcanization.

Instead of adding on the mixing roll the basic materials intended toactivate the compounds or accelerate their action, one may permit thebasic material to diffuse into the rubber. For instance if the stockgiven above for vulcanization in the air be vulcanized in air containingammonia, the vulcanization. is greatly accelerated and the surface ofthe stock is remarkably hard and resistant to marring. The introductionof the basic ma terial may be made on the mill by diffusion from aliquid, solution, or gas, or from adjoining rubber stock or from afabric.

For example a stock containing 100 parts of pale crepe, parts of zincoxide, 3 parts of sulphur and .3 part of 2-6 dinitro-l-chlorophenyldimethyl dithiocarbamate, made up in the usual manner, may be sheetedtosay .060 inches thickness or may be in the form of an article. If thesheet or article be treated with gaseous ammonia for about16 hrs, itwill vulcanize very much more rapidly and at a lower temperature than astock not so treated. Instead of gaseous ammonia, I may employ aqueousammonia, aqueous diethylamine, aqueous aniline or dimethylamine oraniline vapor. It is believed that these basic materials diffuse intothe rubber and accelerate the action of the2-6 dinitrol-chloro phenyldimethyl dithiocarbamate.

As an example of the introduction by difiiusion of the basic material aswell as the introduction by diffusion of'some of the com- 7 stock ismade up of 100 parts of pale crepe,

10 parts of zinc oxide, 3 parts of sulphurjand t parts of dibenzylamine.This stock is mixed on the mills in the usual manner and calendered to athickness of .0107. The two stocks are plied up alternately using 3plies of each and allowed to stand for 2 hours to permit the diffusionofthe dibenzylamineinto the 2-6 dinitrol-chloro phenyl stock and of the2-6 dinitro-z-chloro phenyl dimeth'yl dithiocarbamate into thediben'zylamin'e stock. Thereafter the plied up stock is heated at 2l2andit is found that vulcanization occurs much more quickly than it does forthe individual stocks which have not been plied up. It will be observedthat the dibenz'ylamine acts to neutralize-the monochlor acetic acid aswell as to activate the 2-6 dinitrol-chloro phenyl dimethyldithiocarbamate. 7

As pointed out before the presence-of the monchloracetic acidimprovedthe resistance to burning but the procedure may be carried outwithout the use of the acid.

The basic material (ammonia etc.) may be introduced from the surroundingmedium such as air or water to neutralize the acids and/or to activatethe accelerator. For instance if .2 part of acid be added to the stockfor air cure given above, and the stock be cured in air containingammonia gas the ammonia will not only neutralize the acid but willactivate the 2-6 dinitrol-chloro phenyl compound. The basic material maycement form, etc. before the stock is subjected to vulcanization, or thestock maybe vulcanized in a solution or suspension of the basicmaterial.

Any of these ingredients, base, acid, and

accelerator may be brought together in the T form 01": cements, i. e. acement containing acceleratormay be mixed with a cement containing thebase at the time the cement is to be used. The accelerator cement willnot vulcanize appreciably at ordinary temperatures if the base beabsent. Likewise, asaccelerator-containing cement may be preserved in anunvulcanizedcondition for a long period by the addition of acid (assuch, in solution, or in a cement). When vulcanization is desired, a.base may be added (as such, in solution, or in a cement)a-ndv'ulcanization will then take place.

The compounds in general may be used in amounts varying between and 1part on i;

better is their action with litharge in the .7 absence or presence ofzinc oxide.

All of the above mentioned compounds are accelerators of vulcanization.Some of them give high tensile strength and other valuable physicalproperties such as improved resistance to abrasion, ageing, and otherproperties. The claims are therefore to be broadly interpreted asincluding such treatment of rubber in any form (solid, solution,dispersion) for, thesepurposes as well as for vulcanization, in whichlatter instance, it is understood that a vulcanizing agent and ametallic oxide or its equivalent will be added to the rubber and anantioxidant or other material improving the physical properties of therubber may be present if desired. It is of course understood that notall. of these compounds are of equal accelerating strength, pound forpound, under identical vr'ilcanizing conditions. These accelerators maybe used in conjunction with any of the known antioxidants, ageimprovers,and other materials introduced into rubber. to improve ageingand other physical properties! The rate of reaction-of the compound withsodiumjhydroxide in boiling aqueous alcohol may be determined asfollows:

001% moles of the compound is weighed into a cc. Erlenmeyer; 25 cc.alcohol therefor exactlyBO minutes The solution is then cooled quicklyand titrated with approximately N/lO acid, using phenolphthalen as theindicator. Carbon dioxidet'ree water should be used throughout. A blankshould be run in order to check up on the amount of acid necessary toneutralize the sodium hydroxide when no compound is used. The decreasein hydroxyl ion content during the boiling is taken as a measure of theextent of the reaction with sodium hydroxide.

The above procedure constitutes a method whereby the relative rate ofhydrolysis of any given compound of the types disclosed may be comparedwith that of diphenylmethyl dimethyl dithiocarbamate.

The diphenylmethyl dimethyl dithiocarbamate may be prepared inaccordance with the general procedure indicated herein for the relatedesters of dithiocarbamates, that is, reacting in dilute alcoholicsolution under heat the sodium salt,sodium dimethyl dithiocarbamateandthe chloride of the ester group,diphenyl chloro methane. The separatedoil solidifies on standing and may be purified by recrystallization fromalcohol in the usual manner.

It is known that the rate of hydrolysis of organic compounds, or moreexactly, their rate of reaction with a base such as sodium hydroxide,varies with the substituents in the organic compound. This variation hasbeen utilized in the present invention.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

1. A rubber product derived from rubber combined with a metallic oxide,a vulcanizing agent and a 2-6 dinitro 4 chloro phenyl ester of asubstituted dithiocarbamic acid, which ester is capable of hydrolyzingin aqueous alcohol in the presence of sodium hydroxide at least asrapidly as diphenyl methyl dimethyl dithiocarbamate under the sameconditions.

2. A Vulcanized rubber product derived from rubber combined with zincoxide, sulphur and a 2-6 dinitro 4 chloro phenyl ester of an alkyldithiocarbamic acid, which ester is capable of hydrolyzingin aqueousalcohol in the presence of sodium hydroxide at least as rapidly asdiphenyl methyl dimethyl dithiocarbamate under'the same conditions.

3. A vulcanized rubber product derived from rubber combined with zincoxide, sulphur and a 2-6 dinitro 4 chloro phenyl ester of a dialkyldithiocarbamic acid.

4. A vulcanized rubber product derived from rubber combined with zincoxide, sulphur and a 2-6 dinitro 4 chloro phenyl ester of adisubstituted dithiocarbamic acid.

5. A vulcanized rubber product derived from rubber combined with zincoxide, sulphur and a 2-6 dinitro 4 chloro phenyl ester of an aliphaticsubstituted dithiocarbamic acid.

6. A vulcanized rubber product derived from rubber combined with zincoxide, sulphur and 2-6 dinitro 4 chloro phenyl dimethyl dithiocarbamate.

7. A method of treating rubber which comprises vulcanizing rubbercontaining a metallic oxide and a vulcanizing agent in the presence of a2-6 dinitro chloro phenyl ester of a substituted dithiocarbamic acidwhich ester is capable of hydrolyzing in aqueous alcohol in the presenceof sodium hydroxide at least as rapidly as diphenyl methyl dimethyldithiocarbamate under the same conditions.

8. A method oi treating rubber which comprises vulcanizing rubbercontaining zinc oxide and sulphur in the presence of a 2-6 dinitro 4chloro phenyl ester of an alkyl dithiocarbamic acid, which ester iscapable of hydrolyzing aqueous alcohol in the presence of sodiumhydroxide at least as rapidly as diphenyl methyl dimethyldithiocarban'iate under the same conditions.

9. A method of treating rubber which comprises vulcanizing rubbercontaining zinc oxide and sulphur in the presence of a 2-6 dinitro 4chloro phenyl ester of a dialkyl dithiocarbamic acid.

10. A method of treating rubber which comprises vulcanizing rubbercontaining zinc oxide and sulphur in the presence of a 2-6 dinitro 4chloro phenyl ester of a dissubstituted dithiocarbamic acid.

11. A method of treating rubber which comprises vulcanizing rubbercontaining zinc oxide and sulphur in the presence of 2-5 dinitro 4chloro phenyl dimethyl dithiocarbamate.

12. A method of treating rubber which comprises vulcanizing rubbercontaining zinc oxide and sulphur in the presence of a 2-(5 dinitro 4chloro phenyl ester of an aliphatic substituted dithiocarbamic acid.

Signed at New York, county and State of New York, this 23rd day ofFebruary, 1928.

- SIDNEY M. CAD'WELL.

